форме присваиваю AllowDrop = True. Запускаю

Note You must add the common language runtime support compiler option (/clr:oldSyntax) in Visual C++ 2005 to successfully compile the previous code sample. To add the common language runtime support compiler option in Visual C++ 2005, follow these steps:
Click Project, and then click <ProjectName> Properties.

Note <ProjectName> is a placeholder for the name of the project.
Expand Configuration Properties, and then click General.
Click to select Common Language Runtime Support, Old Syntax (/clr:oldSyntax) in the Common Language Runtime support project setting in the right pane, click Apply, and then click OK.

public ref class Form1 : public System::Windows::Forms::Form //вот это
	{
	public:
		Form1(void)
		{
			InitializeComponent();
			//
			//TODO: Add the constructor code here
			//
		}